This application is based on application No. 10-272308 filed in Japan, the content of which is hereby incorporated by reference.
(1) Field of the Invention
The present invention relates to a multi-beam image recording apparatus which records an image by scanning optical beams, and particularly relates to a multi-beam image recording apparatus that can switch between different resolutions.
(2) Description of Related Art
There have been laser-beam printers employing the electrophotographic method that can switch between different resolutions.
Examples of such a technique for switching between the resolutions are disclosed in Japanese Laid-Open Patent Applications No. 09-54262 and No. 07-9696 and U.S. Pat. No. 5,241,329. Each of these references relates to a so-called xe2x80x9cmulti-beam apparatusxe2x80x9d which scans beams on a surface of a photosensitive drum.
The invention disclosed in Japanese Laid-Open Patent Application No. 09-54262 relates to an apparatus that scans two beams on the surface of the photosensitive drum. In this apparatus, the resolution is switched by changing a distance between the centers of the two beams emitted for scanning, the distance being measured in the sub-scanning direction. This distance is changed by rotating a dove prism disposed on the way of light paths of the two beams or by switching between a plurality of cylinder lenses each having a different focal length.
The invention disclosed in Japanese Laid-Open Patent No. 07-9696 also relates to an apparatus that scans two beams on the surface of the photosensitive drum. In this apparatus, a distance between the centers of the two beams is changed by adjusting an emitting position of one of the two beams in fine increments.
The invention disclosed in U.S. Pat. No. 5,241,329 relates to an apparatus that forms one pixel of image using a plurality of beams aligned in the sub-scanning direction. In this apparatus, the resolution is switched by changing the number of beams to be used for forming one pixel of image. For example, suppose that one pixel of image is formed using three beams now. When the number of beams (three in this case) to be used for forming one pixel of image is reduced to one and the scanning speed is increased three times faster, the pitch can be reduced to one-third. As a result, the resolution can be increased three times higher.
However, each of the apparatuses disclosed in these references needs a special construction for switching the resolution. For the apparatus of the cited Japanese Laid-Open Patent Application No. 09-54262, a rotateable dove prism or a device for switching between the cylinder lenses is required. When the dove prism is used, high precision is required for a driving device that rotates the dove prism. Such a special construction leads to high manufacturing costs.
Also, the apparatus of Japanese Laid-Open Patent No. 07-9696 needs a device for adjusting the emitting position of the beam, and considerably high precision is required for such a device.
Meanwhile, the apparatus of U.S. Pat. No. 5,241,329 needs a plurality of light sources corresponding to the number of resolutions that can be selected. This apparatus employs the method of forming one pixel of image using a plurality of beams. Thus, when forming an image at the lowest resolution, the use efficiency of the light sources is decreased. This is because only one line can be scanned at one scanning operation even though the plurality of light sources are provided.
The first object of the present invention is to provide a multi-beam image recording apparatus which can switch between resolutions without having to include a special construction requiring high accuracy for adjustments or a large number of laser sources.
The second object of the present invention is to provide a multi-beam image recording method by which the resolutions can be switched without a special construction requiring high accuracy for adjustments or a large number of laser sources.
The first object of the present invention can be achieved by an image recording apparatus which records an image by scanning a plurality of optical beams across an image carrier, the image recording apparatus made up of: a storing unit which holds image data to be recorded, as a plurality of sets of line data; a receiving unit which receives resolution data that indicates a resolution of the image data to be recorded; a reading unit which reads sets of line data from the storing unit, the sets of line data being determined according to the received resolution data; a plurality of light emitters which respectively emit optical beams, each optical beam being modulated with a different set of line data read by the reading unit; a main-direction scanning unit which simultaneously scans the optical beams in a main scanning direction, the optical beams being separated from each other on a surface of the image carrier in a sub-scanning direction that is perpendicular to the main scanning direction; a diameter changing unit which changes, in accordance with the resolution data, a diameter of a spot formed by each optical beam on the surface of the image carrier, without changing a distance between the optical beams; and a pitch changing unit which changes, in accordance with the resolution data, a pitch between main-scanning lines on the image carrier in the sub-scanning direction, each main-scanning line being a path of an optical beam that is scanned on the image carrier in the main scanning direction by the main-direction scanning unit.
With this construction, the specified resolution can be realized by changing the diameter of the spot and the pitch as well as determining the sets of line data to be used for modulating the optical beams according to the resolution data. Accordingly, the resolutions can be switched at low costs without reducing the image quality.
The first object of the present invention can be also achieved by an image recording apparatus which records an image by scanning a plurality of optical beams across an image carrier, the image recording apparatus made up of: a storing unit which holds image data to be recorded, as a plurality of sets of line data; a receiving unit which receives resolution data that indicates a resolution of the image data to be recorded; a reading unit which reads sets of line data from the storing unit; a plurality of light emitters which respectively emit optical beams, each optical beam being modulated with a different set of line data read by the reading unit; a main-direction scanning unit which simultaneously scans the optical beams in a main scanning direction, the optical beams being separated from each other on a surface of the image carrier in a sub-scanning direction that is perpendicular to the main scanning direction; and a diameter changing unit which changes, in accordance with the resolution data, a diameter of a spot formed by each optical beam on the surface of the image carrier, without changing a distance between the optical beams.
The first object of the present invention can be also achieved by an image recording apparatus which records an image by scanning a plurality of optical beams across an image carrier, the image recording apparatus made up of: a storing unit which holds image data to be recorded, as a plurality of sets of line data; a receiving unit which receives resolution data that indicates a resolution of the image data to be recorded; a reading unit which reads sets of line data from the storing unit; a plurality of light emitters which respectively emit optical beams, each optical beam being modulated with a different set of line data read by the reading unit; a main-direction scanning unit which simultaneously scans the optical beams in a main scanning direction, the optical beams being separated from each other on a surface of the image carrier in a sub-scanning direction that is perpendicular to the main scanning direction; and a pitch changing unit which changes, in accordance with the resolution data, a pitch between main-scanning lines on the image carrier in the sub-scanning direction, each main-scanning line being a path of an optical beam that is scanned on the image carrier in the main scanning direction by the main-direction scanning unit.
The first object of the present invention can be also achieved by an image recording apparatus which records an image by scanning a plurality of optical beams across an image carrier, the image recording apparatus made up of: a storing unit which holds image data to be recorded, as a plurality of sets of line data; a receiving unit which receives resolution data that indicates a resolution of the image data to be recorded; a reading unit which reads sets of line data from the storing unit, the sets of line data being determined according to the received resolution data; a plurality of light emitters which respectively emit optical beams, each optical beam being modulated with a different set of line data read by the reading unit; and a main-direction scanning unit which simultaneously scans the optical beams in a main scanning direction, the optical beams being separated from each other on a surface of the image carrier in a sub-scanning direction that is perpendicular to the main scanning direction.
The second object of the present invention can be achieved by an image recording method of recording an image by scanning a plurality of optical beams across an image carrier, the image recording method including: a step of storing image data to be recorded, as a plurality of sets of line data; a step of receiving resolution data that indicates a resolution of the image data to be recorded; a step of reading sets of line data from the storing unit, the sets of line data being determined according to the received resolution data; a step of emitting a plurality of optical beams, each optical beam being modulated with a different set of line data read in the reading step; a step of changing, in accordance with the resolution data, a diameter of a spot formed by each optical beam on the surface of the image carrier, without changing a distance between the optical beams; a step of simultaneously scanning the optical beams in a main scanning direction, the optical beams being separated from each other on a surface of the image carrier in a sub-scanning direction that is perpendicular to the main scanning direction; and a step of changing, in accordance with the resolution data, a pitch between main-scanning lines on the image carrier in the sub-scanning direction, each main-scanning line being a path of an optical beam that is scanned on the image carrier in the main scanning direction by the scanning step.
The second object of the present invention can be also achieved by an image recording method of recording an image by scanning a plurality of optical beams across an image carrier, the image recording method including: a step of storing image data to be recorded, as a plurality of sets of line data; a step of receiving resolution data that indicates a resolution of the image data to be recorded; a step of reading sets of line data from the storing unit; a step of emitting a plurality of optical beams, each optical beam being modulated with a different set of line data read in the reading step; a step of changing, in accordance with the resolution data, a diameter of a spot formed by each optical beam on the surface of the image carrier, without changing a distance between the optical beams; and a step of simultaneously scanning the optical beams in a main scanning direction, the optical beams being separated from each other on a surface of the image carrier in a sub-scanning direction that is perpendicular to the main scanning direction.
The second object of the present invention can be also achieved by an image recording method of recording an image by scanning a plurality of optical beams across an image carrier, the image recording method including: a step of storing image data to be recorded, as a plurality of sets of line data; a step of receiving resolution data that indicates a resolution of the image data to be recorded; a step of reading sets of line data from the storing unit; a step of emitting a plurality of optical beams, each optical beam being modulated with a different set of line data read in the reading step; a step of simultaneously scanning the optical beams in a main scanning direction, the optical beams being separated from each other on a surface of the image carrier in a sub-scanning direction that is perpendicular to the main scanning direction; a step of changing, in accordance with the resolution data, a pitch between main-scanning lines on the image carrier in the sub-scanning direction, each main-scanning line being a path of an optical beam that is scanned on the image carrier in the main scanning direction by the scanning step.
The second object of the present invention can be also achieved by an image recording method of recording an image by scanning a plurality of optical beams across an image carrier, the image recording method including: a step of storing image data to be recorded, as a plurality of sets of line data; a step of receiving resolution data that indicates a resolution of the image data to be recorded; a step of reading sets of line data from the storing unit, the sets of line data being determined according to the received resolution data; a step of emitting a plurality of optical beams, each optical beam being modulated with a different set of line data read in the reading step; and a step of simultaneously scanning the optical beams in a main scanning direction, the optical beams being separated from each other on a surface of the image carrier in a sub-scanning direction that is perpendicular to the main scanning direction.